Recent concern for environmental issues such as global warming has led to an increasing social demand for lower fuel consumption. In order to respond to the demand for lower fuel consumption automobiles, development of fuel efficient tires with reduced rolling resistance is being required. Known as methods for reducing the rolling resistance of tires in terms of materials are, for example, a technique of replacing carbon black with silica, a technique of reducing the amount of filler which causes energy loss, and a technique of using a modified rubber having a functional group which is highly reactive with silica.
Although the above techniques can improve the performance in terms of rolling resistance, the reduction in the amount of filler and the use of the modified rubber each tend to cause reduction in rubber strength. Further, if the modified rubber is used, it needs to be kneaded enough to sufficiently react with silica. As a result, the surface of the rubber composition is made rough so that the adhesive force (adhesion) is reduced, which results in a decrease in the building processability of tires.
In order to improve the adhesion and the rubber strength, the use of aliphatic petroleum resin or aromatic petroleum resin has been studied; however, these uses disadvantageously deteriorate the fuel economy. Patent Document 1 teaches a method of improving the fuel economy and braking performance by use of natural rubber, white filler, a specific resin, and the like. This document, however, does not discuss satisfying the fuel economy, processability, adhesion, and rubber strength simultaneously.    Patent Document 1: JP 2009-7454 A